Although progress has been made in survival of patients with earlier stage colorectal cancer (CRC), only minimal improvement has been noted in patients with systemic metastases (Stage IV disease). Current chemotherapeutic agents, while highly effective at killing CRC cells, are limited by their systemic toxicity. If advances ar to be made in the survival of cancer patients, highly innovative strategies are required for more targeted delivery of anti-cancer agents directly to CRC metastases. Our ultimate translational goal is to develop a highly effective and less toxic approach to specifically deliver anti-cancer agents to CRC metastases. To achieve this goal, we have assembled a multidisciplinary and highly collaborative team who are at the forefront of molecular signaling pathways in CRC, CRC treatment modalities, medicinal chemistry, novel nanoparticle synthesis and delivery systems. Over the last two years, we have made significant progress to achieve our goals: (i) using a novel three-way junction (3WJ) motif, we have constructed thermodynamically and chemically stable three-branched RNA nanoparticles with an aptamer against receptors that can deliver a small molecule inhibitor or chemotherapeutic agent specifically to CRC metastases in the liver, (ii) we have constructed a variety of RNA nanoparticles using the pRNA-3WJ motif as a scaffold and have demonstrated in critical experiments that the resulting RNA constructs retained their folding and independent functionalities for specific cell binding, cell entry and cancer targeting, both in vitro and in vivo, (iii) we have shown that the RNA nanoparticles remain intact after systemic injection into mice and strongly bind to tumors with little accumulation in normal organs or tissues; these RNA constructs are non- toxic, non-immunogenic, and display favorable pharmacological profiles in mice, and (iv) we have demonstrated localized in vivo delivery of pRNA-3WJ to CRC xenografts and liver metastases. Thus, the central hypothesis of our proposal is that CRC receptor-specific delivery of chemotherapeutic agents using our pRNA-3WJ nanoparticles will provide a safe, effective strategy to selectively target and inhibit CRC metastasis. To address our hypothesis, we have designed experiments with the following Specific Aims: 1) to construct pRNA-3WJ nanoparticles coupled with anti-cancer agents and analyze their stability, cellular uptake and anti-proliferative effects in vitro; 2) to determine te pharmacokinetics, stability, safety and drug delivery of pRNA-drug conjugates in vivo; and 3) to evaluate the selective delivery and in vivo anti-tumor effect of pRNA- 3WJ nanoparticles coupled with anti-cancer agents. In summary, our enthusiasm for our current proposal is driven not only by its inherent scientific importance, but also by its translational potential, clinical impact, and the possibility to provide a more effective and less toxic delivery system targeting CRC metastases.